Short-term responses of glass eels transported from UK to small Belgian streams

Abstract

-Restocking of inland waters with glass eels is one of the recovery options to prevent the decline of European eel Anguilla anguilla (L.) populations. We studied the growth, dispersion, density and habitat preferences in the imported glass eels from UK and stocked in three typologically different small Belgian streams, using electrofishing surveys around the single release point, 1 year following stocking. Our results clearly support that the recaptured individuals stocked in our streams farther from the sea, survived, grew, dispersed upstream and downstream. Elvers exploited the complete transversal section of stream, with preference for the sheltered microhabitats near the banks with slower water velocity and low depth. Length-weight relationship was different between streams in terms of allometric coefficient (b). We assume that microhabitats and food availabilities lead to contrasted results in terms of growth and absolute occurrence. Restocking of glass eels in small middle-land streams was found to be an interesting and unconventional option that requires adequate stream and habitat selection.

Dynamics of upstream movements of the European eel Anguilla anguilla in an inland area of the River Meuse over the last 20 years

“…Particularly in the River Meuse, the upstream habitats are no longer colonized by eels and will therefore be emptied of this fish species when the last resident eels migrate to spawn. In this context, eel conservation actions such as well-targeted glass eel stocking to enhance yellow eel abundance may be necessary conservation measures, if adequately carried out (Ovidio et al 2015;Brämick et al 2015).…”

What happens to glass eels after restocking in upland rivers? A long‐term study on their dispersal and behavioural traits

“…The Mosbeux River is a typical trout zone, and the Vesdre River is a barbel zone (Huet, ). This study site was selected because it was subjected to the restocking of glass eels ( n = 4155) in 2013, which were released at a single point in the Mosbeux River, 0.040 km upstream of its mouth (Ovidio et al, ). During the study period (from 2014 to 2017), the observed mean width and depth of the Mosbeux River were 2.40 and 0.18 m, respectively, compared with 14.90 and 0.44 m, respectively, for the Vesdre River.…”

“…Electrofishing (EFKO, 3.0 kVA) using hand nets with a 40 × 40 cm diameter and 2 × 2 mm mesh was used to capture the small restocked eels, following the technique used by Ovidio et al (). From November 2014 to September 2016, nine electrofishing sessions (S 1 –S 9 ) were performed (Table ).…”

“…As artificial reproduction of the European eel is not yet possible, the only source of restocking material is the translocation of wild‐caught glass eels or elvers (Pedersen & Rasmussen, ). Many studies have reported encouraging outcomes, such as the restocked young eels surviving (with a survival rate of 3.5–20% reported by Shiao, Lozys, Iizuka, & Tzeng, ; with a survival rate of 5–45% reported by Simon & Dörner, ) and growing (with growth in streams of 0.5–10.5 cm year −1 reported by Ovidio et al, ; with growth in lakes of 0.9–9.3 cm year −1 reported by Pedersen, and Simon et al, ; and with growth in lagoons of 5.5–8.3 cm year −1 reported by Lin, Lozys, Shiao, Iizuka, & Tzeng, ) in their novel environments. Most of these studies were conducted in the short term, dealing with restocking efficiency in growth and survival (Andersson, Sandström, & Hansen, ; Bisgaard & Pedersen, ; Lin et al, ; Pedersen, ; Simon & Dörner, ).…”

“…Under such conditions, restocking using young life stages remains a solution to enhance the local stocks of eels and to conserve the species in the upper parts of rivers, and probably over the long term to meet the silver eel escapement target in the Eel Recovery Plan of the European Union (Council of the European Communities, ). Restocking using glass eels and elvers is one of the recovery options identified by the European Commission for habitats with low or no natural immigration (Ovidio, Tarrago‐Bès, & Nzau Matondo, ; Simon, Dörner, & Richter, ; Simon, Dörner, Scott, Schreckenbach, & Knösche, ). As artificial reproduction of the European eel is not yet possible, the only source of restocking material is the translocation of wild‐caught glass eels or elvers (Pedersen & Rasmussen, ).…”